An investigation has been launched after a mother and her small child discovered the floor of a train toilet compartment was missing.
She caught hold of her child to stop him falling on to the exposed train wheels, according to the UK's Rail Accident Investigation Branch (RAIB).
They were both reportedly left shocked and the child suffered minor bruising, investigators said.
The incident occurred on the South Devon Railway heritage line between Staverton and Buckfastleigh, England on June 22.
Engineers had dismantled the floor during repairs to the carriage's braking system.
Staff had placed a notice on the compartment door and attempted to secure it to prevent it being opened, but "this had not been effective", the RAIB said.
The investigation will examine the events leading up to the incident and the railway's safety management system.